How to Convert String to JSON Object in Java?

In contemporary Java development, handling JSON data is a typical activity. To manipulate data effectively, one must be able to transform JSON strings into Java objects. To accomplish this conversion, we will examine three popular open-source libraries in this guide: Gson, JSON-Simple, and Jackson. We'll also walk through a practical example of creating a Java object from a JSON-like string without the need for outside libraries.

JSON Overview

A popular lightweight data transfer format for web development and data communication is JSON or JavaScript Object Notation. Both humans and machines can easily grasp it thanks to its human-readable format. This is an example of a JSON structure:

JSON Format

{
  "employee": {
    "id": 101,
    "name": "John Doe",
    "position": "Software Engineer",
    "skills": ["Java", "Python", "JavaScript"],
    "contact": {
      "email": "john.doe@example.com",
      "phone": "+1-123-456-7890"
    },
    "projects": [
      {
        "projectName": "Project A",
        "durationMonths": 6,
        "technologiesUsed": ["Java", "Spring Boot"]
      },
      {
        "projectName": "Project B",
        "durationMonths": 8,
        "technologiesUsed": ["Python", "Django"]
      }
    ]
  },
  "company": "TechCo Inc.",
  "location": "Cityville"
}

Convert JSON String to JSON Object

There are the following three libraries are used to convert String to JSON Object in Java:

Using Gson Library
Using JSON-Simple Library
Jackson Library

Using Gson Library

Gson is a powerful Java library provided by Google for handling JSON data. It allows easy conversion between JSON Strings and Java objects.

The following line of code is used to convert JSON String to JSON Object.

Gson g = new Gson();
Student s = g.fromJson(jsonString, Student.class)

We can also convert JSON Object to JSON String by using the toJson() method.

Using JSON-Simple Library

An additional free Java package for converting JSON String to JSON Object is this one. The JSON-Simple library has the benefit of being compact in size. When there is a memory constraint, it works perfectly. Keep in mind that JDK 1.2 is also compatible with it. This indicates that it can be utilized with legacy Java 5 projects. To convert the JSON String to JSON Object, we use the following commands.

JSONParser parser = new JSONParser();
JSONObject json = (JSONObject) parser.parse(stringToParse);

Using Jackson Library

A popular and effective Java library for mapping Java objects to JSON and vice versa is the Jackson library. It performs quickly, has a tonne of features, and allows streaming. The stream can parse large JSON outputs from online services without needing to be entirely loaded into memory. The JSON String that represents a student is converted into a Java class that represents the student in the following statement.

Jackson Library's drawback is that it needs at least JDK 1.5. Therefore, it won't fit there if we're working with an older version. The library's lack of J2ME functionality is yet another drawback.

StringToJsonExample.java

import java.util.HashMap;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class StringToJsonExample {
    public static void main(String[] args) {
        // Original JSON String
        String jsonString = "{\"name\": \"John\", \"age\": 25, \"city\": \"New York\"}";
        // Convert JSON String to JSON Object
        Map<string , object> jsonObject = convertStringToJsonObject(jsonString);
        // Display the converted JSON Object
        displayJsonObject(jsonObject);
    }
    // Method to convert JSON String to JSON Object without using external libraries
    private static Map<string , object> convertStringToJsonObject(String jsonString) {
        Map<string , object> jsonObject = new HashMap<>();
        // Use regular expression to extract key-value pairs
        Pattern pattern = Pattern.compile("\"(\\w+)\":\\s*\"?([^\"]*)\"?");
        Matcher matcher = pattern.matcher(jsonString);
        while (matcher.find()) {
            String key = matcher.group(1);
            String value = matcher.group(2);
            // Handle different value types (string, number, boolean)
            if (value.matches("\\d+")) {
                jsonObject.put(key, Integer.parseInt(value));
            } else if (value.equalsIgnoreCase("true") || value.equalsIgnoreCase("false")) {
                jsonObject.put(key, Boolean.parseBoolean(value));
            } else {
                jsonObject.put(key, value);
            }
        }
        return jsonObject;
    }
    // Method to display JSON Object
    private static void displayJsonObject(Map<string , object> jsonObject) {
        for (Map.Entry<string , object> entry : jsonObject.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}
</string></string></string></string></string>

Output:

name: John
age: 25

Explanation

The extracted key-value pairs are stored in a HashMap called jsonObject, which is initialized by the convertStringToJsonObject method. The key and value components of each pair are matched and captured using a regular expression pattern. A Matcher is then used to apply the pattern to the input JSON string. The function iterates through the matches, extracts the value and key, and then adds the appropriate data to the JSON object. During this procedure, various value types-such as strings, numbers, and booleans-are handled correctly. Every key-value pair is printed by the displayJsonObject method, which iterates over the entries in the jsonObject. This guarantees a legible presentation of the transformed JSON object.

Conclusion

In summary, the Gson package makes it easier to convert JSON data into Java objects. It offers a clear and simple method for working with JSON in Java programs. Especially when working with real-world settings where JSON data may not always match the intended structure, be sure to handle exceptions appropriately.

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